Wells of various types after their useful lives are shut down and usually permanently plugged for a variety of reasons. Frequently, depleted hydrocarbon producing wells are required by laws to be permanently plugged for protecting aquifers and the above surface environment.
Regulations exist for plugging abandoned wells to protect both below and above surface environments and to prevent accidents from occurring at the plugged well. Such regulations often require that the plugs have a certain minimum strength and maximum liquid permeability. Governmental agencies often are required to inspect and approve hydrocarbon well closures before the wells can be officially certified as closed. For example, in the State of California the certifying agency is the Department of Conservation, Division of Oil and Gas.
Although approved well-closure compositions exists, since permanently plugged wells are no longer a source of income, there is a strong economic incentive to permanently plug such wells as cheaply as possible. This invention is directed to cheaper cementitious compositions for permanently plugging wells, processes of preparation of such compositions, processes for applying such compositions, and methods having advantages of reducing the costs of such operations including estimating cost and markup or bid prices.
In the abandonment of hydrocarbon wells, hydraulic cementitious slurries are used to create hard plugs in the wellbore which are effective for permanently closing the well. Specialized equipment is used to inject the slurry into the well at surface level. Under pressure the slurry is forced to the bottom of the well and into the subterranean porosity zone. As the slurry fills in at the well bottom, sufficient resistance is met to cause the slurry to lift vertically towards the surface. Based on the diameter and depth of a given well, the volume of hydraulic cementitious slurry required to close a particular well can be calculated. The slurry must produce upon curing a vertical hard plug to a level of 100 ft. above the subterranean porosity zone.
The performance of a given slurry mix for hydrocarbon well closure is required to meet the American Petroleum Institute (xe2x80x9cAPIxe2x80x9d) specification for a competent hard plug. As defined by API, a hard plug must meet and maintain a compressive strength of 1000 psi and have a maximum permeability of 0.1 millidarcy (xe2x80x9cmdxe2x80x9d).
Many hydrocarbon production companies contract well abandonment work to service organizations that specialize in well closure services. These service organizations use approved cementitious materials in the slurry mixes for placing and forming the competent hard plugs. G series Portland cement and minus 200 sieve silica product are currently approved materials for well plug slurries. By the term xe2x80x9csilica productxe2x80x9d as used herein is meant a solid material whose major component is silica and is widely used in hydraulic cements. Generally in such silica products the amount of silica exceeds about 95% and is usually about 98% to about 99%. As used herein, the term silica product does not included cement kiln dust (xe2x80x9cCKDxe2x80x9d). These materials are relatively high cost products individually when compared to the dry cementitious solids of this invention. A typical silica product suitable for forming hydraulic cementitious slurries is from about minus 90 mesh silica sand to about minus 200 mesh silica powder.
In current conventional well abandonment operations, G Series Portland cement is obtained from cement manufacturers and the silica product from other manufacturers at other locations. Transportation cost from two different locations are incurred. Before the cement and silica product are used to form the hydraulic cementitious slurry they must be blended, and thereafter slurried with water, before pumping down the well, as illustrated in FIG. 1.
Accordingly, this invention is directed to less costly dry cementitious solids for slurry use and a process for blending such dry cementitious solids which have the advantage of greatly reducing the cost of hydrocarbon well abandonment and closing.
In general this invention is directed towards dry cementitious solids comprising cement kiln dust (xe2x80x9cCKDxe2x80x9d) and cement: hydraulic cementitious slurries produced from such dry cementitious solids; the solid cementitious compositions resulting from the curing of such hydraulic cementitious slurries; processes for making and using such materials; methods of blending the dry cementitious solids prior to slurrying; and methods for estimating and reducing cost and estimating price markup in well closure operations using the CKD-containing formulations of this invention.
CKD is a waste material generated in cement manufacture. CKD is a partially calcined kiln feed which is removed from the gas stream and collected in a dust collector. Chemical analysis of CKD from cement manufacturers usually varies depending on the particular feed. Variations also exist from one manufacture to another depending in part on the efficiencies of the cement production operation and the associated dust collection systems. Typically, the major oxides found in CKD""s are SiO2, Al2O3, Fe2O3, CaO, MgO, SO3, Na2O and K2O. Chemical analysis of some CKD""s are found in U.S. Pat. Nos. 4,432,800 and Re. 33,747 which are hereby incorporated herein by reference. Such variations, however, do not have any detrimental effects on the usefulness and performance of this invention.
CKD is available from a number of cement manufacturers at a price significantly lower than the cost of materials currently being used in cementitious slurries for hydrocarbon well closures. Type II Portland cement is cheaper than G Series Portland cement by about $2.00 per ton based on raw cost. Since the resulting hard cores produced by this invention using Type II Portland cement meet or exceed all requirements of API for a competent hard plug, Type II Portland cement is preferred only for achieving better economics. Of course, if desired the more expensive G Series Portland cement can also be used. In fact, any type of cement can be used in this invention.
In the economics of hydrocarbon abandonment service contracts, the profits are determined by a charged cost per cubic foot (xe2x80x9ccfxe2x80x9d) of slurry, which in turn is determined by the choice of materials, the transportation cost, and the blending cost. This invention is also directed to processes for reducing the cost of well closures.
CKD is made available by a number of cement manufactures so that both the CKD and the cement can be obtained from the same source essentially at the same source location thereby reducing transportation cost. CKD is often regarded as a waste product of the cement industry having limited use elsewhere.